The present invention relates to a device and method for the non-invasive treatment of biological tissue, and in particular, the invention relates to a device and method for treating sciatica via ultrasonic heating focused on a focal area within an intervertebral disc, preferably on the nucleus pulposus, thus degenerating the tissue in the focal area, reducing pressure, and eliminating/reducing pain along the sciatic nerve.
The lifetime prevalence of sciatica is 40 percent, and 1-2 percent of the population will develop nerve compression by a lumbar disc herniation which requires invasive (surgical) treatment, usually during the fourth and fifth decades of life. Surgical removal of discal hernia, known as a discectomy, has been performed for almost seven decades. Diagnostic procedures ranging from myelography using oil, or nonionic contrast media, to computerized tomography (CT) and magnetic resonance imaging (MRI) has led to a rapid increase of the number of spinal operations with a diversity of surgical procedures.
There are four necessary prerequisites for intervention of disc herniation. First, the patient must experience functionally incapacitating pain in the leg extending below the knee with a nerve root distribution. Second, the nerve root must exhibit tension signs with or without neurological abnormalities. Third, the patient must experience failure of clinical improvement after four to eight weeks. Finally, the diagnoses must be confirmed (e.g. through imaging study).
The introduction of non-surgical or minimal invasive surgical procedures started in 1964 with chymopapain and chemonucleolysis which brought about the era of percutaneous treatment for herniated discs. The clinical success of chymopapain, which has good results in 60-75 percent of treatments, led to its extensive use. Unfortunately, it has an anaphylaxis rate estimated to be about 1 percent. The enzyme polymerizes the long chains of proteoglycans in the nucleus pulposus with subsequent loss of water binding capacity. This causes reduction in the volume and pressure of the nucleus pulposus, and results in a reduction in volume and pressure of the herniated fragment resulting in the immediate relief of sciatica in patients following chemanucleolysis. Most authors agree that relief of leg pain after chymopapain is less frequent than after surgery.
Several new methods using percutaneous techniques have evolved since 1975. Initially, these methods used endoscopic equipment. More recently, non-endoscopic techniques have been developed which use an automated percutaneous suction of tissue by means of a probe. Most recently, laser radiation (typically electromagnetic), created by external stimulation of a laser medium, has been used. Laser radiation treatment, however, requires a probe and is therefore invasive.
All these methods are to a certain extent invasive requiring surgical intervention. Disc infection and nerve root injury are potential complications of these methods. Although such complications are not as common as complications resulting from open surgery, they are an unnecessary risk.
The intervertebral disc is comparable to other non-vascularized biological tissue. It has a central nucleus pulposus with a gelatinous character and a surrounding stiffer anulus. The matrix in the disc includes several proteins with different rates of turn over and energy demand.
Currently, there is no non-invasive treatment available which will affect the disc in such a manner to reduce the volume and pressure in the nucleus pulposus thereby diminishing a discal hernia.
Attempts to achieve tissue degeneration with high intensity focused ultrasound (HIFU) have been going on for several years in cancer research projects. The advantage of ultrasound as a generator of energy, compared to, for example electromagnetic fields, is that ultrasound is a noninvasive method used to generate tissue heating at depths within the body. Focusing of the ultrasound, and placing the focus inside the tissue to be treated, makes the heating effect to develop at the desired location instead of at the skin and the tissue in between. Lele P., "Introduction of deep, local hyperthermia by ultrasound and electromagnetic fields. --Problems & Choices", Radiation and Environmental Biophysics 1980; 17: 205-217. If the transducer surface is spherical, the transducer has a fixed focus. Lele P., "Introduction of deep, local hyperthermia by ultrasound and electromagnetic fields. --Problems & Choices", Radiation and Environmental Biophysics 1980; 17: 205-217. It is also possible to achieve a flexible focus by means of phased array. Diederich C., Hynynen K., "The feasibility of using electrically focused ultrasound arrays to induce deep hyperthermia via body cavities", IEEE transactions on ultrasonics, ferroelectrics, and frequency control 1991; 38 (7): 634-643; Ebbini E., Cain C., "Asherical-Section Ultrasound Phased Array Applicator for Deep Localized Hyperthermia", IEEE Transactions on Biomedical Enfineering 1991; 38(7): 634-643; Ebbini E., Umemura S., Ibbini M., Cain C., "A cylindrical-section ultrasound phase-array applicator for hyperthermia cancer therapy", IEEE transactions on ultrasonics, ferroelectrics, and frequency control 1988; 35(5): 561-572; Holmer N., Lindstrom K., "Fr.ang.n A-mode till Phased array i Diagnostiskt ultraljud-Grunderna", editerad av Holmer, 65-67.
Prior art also includes numerous patent specifications relating to methods and devices in which ultrasound is utilized for various therapeutic purposes without any type of surgical operations on the patient. One such patent specification is U.S. Pat. No. 5,435,311 relating to an "ultrasound therapeutic system" for treatment of tissue, such as malignant tumors or various types of calculi like gallstone, kidney stone, etc. The device of U.S. Pat. No. 4,787,394 relating to an ultrasound therapy apparatus, has a similar purpose. Furthermore, other devices and methods utilizing ultrasound for a corresponding therapeutic purpose, are described in U.S. Pat. Nos. 5,327,884 and 5,501,655.
Similar tissue degeneration, as with ultrasound, can also be made with other methods, such as percutaneous laser discectomy and percutaneous radio-frequency coagulation by means of cauterizing instruments, however these methods are invasive. Buchelt M., Kutschera H., Katterschafka T., Kiss H., Schneider B., Ullrich R., "Erb.YAG and Hol.YAG Lasser Ablation of Meniscus and Intervertebral discs", Lasers in Surgery and Medicine 1992; 12: 375-381; Troussier B., Lebas J., Chirossel J., Peoc'h M., Grand S., Leviel J., Phelip X., "Percutaneous Intradiscal Radio-Frequency Thermocoagulation--A Cadaveric Study", Spine 1995; 20(15), 1713-1718.